A pure substance cannot occupy any arbitrary point on the P,T, v space, instead being confined to a surface (i.e., any two that are identified specify the third).
For this reason, one often visualizes the phase behavior of a species by taking a projection of the PvT spaces in two dimensiones: typically in the P-v or P-T plan.
A PT diagram shows the phase behavior of a single species in the pressure-temperature plane. Here, lines denote the boundaries between phases (or the points where the phases coexist).
The saturation pressure is the coexistence pressure between liquid and vapor for a pure species and is a function of temperature (only). (see state postulate)
While the vapor pressure is similar to the saturation pressure, the vapor pressure refers to the pressure in a mixture of components (i.e., the total pressure is higher).
Describe the difference between the saturation and vapor pressures
Coexistence on a Pv diagram is shown on the liquid-vapor dome, since v is very different for liquids and vapors (up to the critical point!).
Coexistence on a Pv diagram is shown on the liquid-vapor dome.
A supercritical fluid is a substance which is above its critical temperature, Tc. Here there is no vapor-liquid transition so the liquid-vapor dome ends.
On the vapor-liquid line the temperature is called the boiling point and the pressure is the vapor pressure.
On the vapor-solid line the temperature is called the sublimation point.
On the liquid-solid line the temperature is called the freezing/melting point.
Identify the phases present on a PT and/or Pv diagram as well as the critical point and triple point